Animal feeds are supplemented with individual amino acids in accordance with the animals' requirements. For supplementation of animal feeds, the amino acids L-lysine, L-valine, L-methionine, L-tryptophan or L-threonine are often used. In particular, for supplementation with L-lysine, L-lysine monohydrochloride with a L-lysine content of 78% was hitherto mainly used. Since L-lysine is produced by fermentation, for production of the monohydrochloride it must first of all be separated from all other components of the crude fermentation broth in laborious process steps, then converted to the monohydrochloride and the latter crystallized. During this, a large number of side products and the reagents necessary for the work-up accumulate as waste.
Since high purity of the animal feed supplement is not always necessary and moreover nutritionally active reusable substances are often contained in the side products of the fermentation, there has therefore been no lack of attempts in the past to convert L-lysine or also other fermentatively produced L-amino acids such as L-valine, L-methionine, L-tryptophan or L-threonine together with components of the fermentation broth into a solid animal feed more inexpensively.
The complex composition of such media has proved to be a disadvantage in processing. These can in general only be poorly dried, and the dried products are often hygroscopic, practically unpourable, liable to caking and unsuitable for the technically demanding processing in mixed feed plants.
The products from the fermentation for the production of lysine are in particular to be mentioned here. The combined dewatering and shaping of the crude fermentation broth by fluidized bed spray granulation drying results in easily handled granules which can be used in this form as animal feed.
Processes for granulation of amino acid-containing animal feed additives based on fermentation broth are known from the documents US 2007/0082031 A1, U.S. Pat. No. 6,126,972 A, US 2010/0304449 A1, U.S. Pat. No. 5,840,358 A and US 2005/0025878 A1.
Ever higher requirements are being set by the market on feed amino acids in the form of solids as regards their bulk material properties. Thus the products created should be dust-free and satisfactorily pourable, and have a narrow particle size distribution and as high as possible a bulk density. In addition, they should be highly stable to abrasion and have reduced hygroscopicity.
US 2005/0025878 A1 and US 2010/0304449 A1 describe the granulation of amino acid-containing and biomass-containing fermentation broths with different compositions and also downstream modified components in the stationary and the circulating fluidized bed.
Essentially, suitable granules are admittedly obtained with fluidized bed spray granulation, but the need to increase output in industrial production processes has the effect that the properties of the granules produced can again deteriorate and are no longer optimal for use. These granules are further processed, for example further dried and cooled, in process steps downstream of the fluidized bed spray granulation.
CN 102274703 A describes such a fluidized bed spray granulation process with downstream process steps for further drying and product cooling. After the fluidized bed spray granulation, the granules obtained are sieved in order to remove the oversize, which comprises the particle sizes which lie above a desired particle size. The remaining granules are further dried in a fluidized bed drying step and cooled. At the same time, in the fluidized bed drying the dust fraction is discharged with the fluidized bed gas. The sieved oversize is comminuted with a crusher and again fed into the fluidized bed spray granulation. Also, the separated dust fraction is dissolved again and sprayed into the fluidized bed granulation chamber. However, due to the reintroduction of the comminuted oversize and the dust fraction into the fluidized bed spray granulation, the throughput in the fluidized bed spray granulation is markedly increased, or in other words the high content of reintroduced particles decreases the capacity of the overall process.
DE 30 07 292 A1 (GB 2 046 121 A) discloses a fluidized bed spray granulation process without subsequent further drying step. Solutions or suspensions of solids to be recovered are sprayed on a hot gas fluidized bed and the particulate material formed in the bed is simultaneously subjected to a grinding process so that in a single step, in a single apparatus particulate material of predetermined particle size distribution is produced. However, this one step process without additional drying step is suitable for rather pure crystalline material, such as salts, metal oxides, urea or sugars. However, such a one step process is not suitable for the granulation of amino acid containing fermentation media with complex compositions which are often hygroscopic and tend to caking. As outlined above, the hygroscopic, not completely dried particulate material obtained in a fluidized bed spray granulation step often requires an additional subsequent drying step.